Watch for surrender flags in corn fields suffering from high temperatures

Sunday’s forecast from the National Weather Service eased up on the corn cooking temperatures, and added some chance of precipitation, at least enough for the Sunday night futures market to head downward instead of upward. However, oven-like temperatures will be curling corn leaves, interrupting pollination and aborting some tip kernels for the next few days. Let’s get to the details.

With the weather maps showing red temperatures, there is not much chance for precipitation, despite the fact corn needs three to four tenths of an inch of water per day during pollination. Pollen and silks are predominantly water, and Iowa State corn specialist Roger Elmore says both moisture and temperatures are important. He’s particularly concerned about the relatively high overnight temperatures, because cool mornings are what triggers pollen shed. Over this week and next an estimated 85% of the US corn crop will be pollinating.

The National Weather Service forecast issued Sunday calls for Cornbelt temperatures to be above normals. The Climate Prediction Center says, “Temperatures are likely to be in the warmest one-third of all years in the eastern three-fourths of the 48 states and very likely to be in the warmest one-third in the eastern Cornbelt.” IA St. meteorologist Elwynn Taylor says, “This type of temperature cycling is typical of strong La Niña conditions and may be the last extreme cycle as the La Niña event diminished to neutral conditions July 1.

So is this a parallel of 1988? Elwynn Taylor says, no, because the drought began earlier in the growing season in 1988. But he’s still concerned about the balance of the growing season, “A point of concern is the forecast distribution of the warm temperatures: warmer than usual in the East and cooler than usual in the West with the transition approximately at the Continental Divide. Such distributions tend to persist for up to six weeks and consistently result in below trend corn yield for the U.S. as was the case in 2010.”

When there is a lack of moisture, but an abundance of heat, what happens to the corn plant? Roger Elmore at Iowa State says there are two impacts, 1) Corn with rolled leaves will lose 1% of yield every 12 hours, except when pollinating, when yield is cut 1% every 4 hours of leaf rolling, 2) an additional 1% yield loss per day if leaves remain rolled for 4 consecutive days, on the sixth day of rolled leaves that yield loss climbs to 4% per day.

While the heat will be impacting nearly the entire Cornbelt, there is a strip of several hundred thousand acres that is doubly affected. That is the region where the derecho winds last Monday laid waste to corn fields, farmsteads, and even grain elevators. While the winds were tracked from Central Nebraska into the Province of Ontario, some particularly heavy facility damage occurred between Marshalltown and Cedar Rapids, Iowa.

However, corn was flattened and with the heat settling in for the week, there are uncertainties how the disabled crop will react. The corn apparently had strong enough stalks to avoid green snap, says IL agronomist Emerson Nafziger. With some roots pulled out and leaves disoriented, it is difficult to predict the potential for yield loss, but it may not be as bad as it looks. And he adds, such a situation slows the water uptake and it may help roots re-establish themselves.

As flattened corn proceeds through its pollination process, agronomists do anticipate some degree of “goosenecking” as the top of the plant attempts to return to a vertical orientation. However, those corn plants will not totally recover, and will likely become a harvest nightmare. They have already become a problem for seed companies which may have lost many of their fields in the affected area.

Watch for USDA’s Crop Progress Report on Monday afternoon to learn however crop statisticians in the affected states begin to evaluate the damage from the winds.

Summary: Weather conditions for the coming few days will not be friendly to corn, particularly corn that is going through the pollination phase. High nighttime temperatures will hamper pollen shed, and curled leaves will hamper sunlight reception; both of which have a substantial impact on potential yield. Corn that was flattened by the severe winds of last week will likely be trying to regain a vertical orientation by “goosenecking,” but yields will still be reduced.